The building trade and related industries consume many square feet annually of forest product materials which require protective or decorative coatings. One of the most used forest product materials is hardboard which is made from ground or chipped wood fibers mixed with a suitable cohesive and pressed. The hardboard surface is coated to improve stain resistance, water and solvent resistance, hardness, and to impart aesthetic value, and for exterior applications, such as siding, to impart weather resistance. Typically, the coating systems have been solvent-based resin compositions. The use of such compositions requires extra safety and health precautions to reduce solvent escape into the air. A water-based coating composition would be less toxic and less polluting.
The use of thermoset resins with an acrylic ester or a polyvinyl chloride latex is generally known (see U.S. Pat. Nos. 2,450,902; 2,600,681; and 2,906,724). The mixture of a typical acrylic ester latex with a polyvinyl chloride latex does not yield a coating composition suitable for application using standard industrial finishing methods due to poor resistance of the deposited film to water and solvents. It was unexpectedly found that a combination of specific ingredients produces a superior water-based coating composition.